How do I adjust opacity of an "image as a plane" in Version 2.90.1?
When selecting your image plane, navigate to the image section of the properties side bar and click on the transparency button to enable it, then adjust the opacity to your desired value.

Alternatively, if you are using the add-on version of images as planes, and still wish to see your image in the final render, you can modify your shader like this, and use the &quot;fac&quot; slider to adjust transparency.